A radio communication system that employs a duplex transceiver typically employs a transceiver radio frequency (RF) self-diagnostic testing system that mixes a transmitter output with a fixed local oscillator output to obtain a signal with a frequency band of approximately 800 MHz to test for proper operation of a receiver. Present such systems utilize only the frequency band at approximately 800 MHz for which a single transmit to receive (T/R) frequency spacing is defined, and thus utilize a particular matched difference frequency loopback oscillator system based on that desired T/R spacing.
At ultra-high frequencies (UHF) and very high frequencies (VHF) no such fixed spacing is defined for present systems. Thus, selection of a self-diagnostic testing system that utilizes other than an approximately 800 MHz frequency band would require matching of a difference frequency loopback oscillator system individually with each selected channel transmission/reception (T/R) frequency spacing. Thus, selection from an unlimited number of T/R frequency spacings would require an unlimited number of loopback systems. Even provision of selection from a number of T/R frequency spacings would require an unwieldy number of loopback systems. Thus, there is a need for a transceiver self-diagnostic testing system that, while providing for selection of a plurality of channel transmission/reception (T/R) frequency spacings, also minimizes a need for a large number of loopback systems.